Combinations of zinc pyrithione and cuprous oxide are known to be excellent antifouling agents when formulated into Paints and paint bases (i.e., the paint before pigment addition) also containing rosin, as disclosed, for example, in U.S. Pat. No. 5,057,153. Unfortunately, however, such paints have now been found to thicken or gel unacceptably within a few days, at best, or a few hours, at worst, when formulated with typical commercial grades of zinc pyrithione in combination with cuprous oxide.
Heretofore, the only solutions to the problem of gellation of paints containing rosin and zinc pyrithione in combination with cuprous oxide, known to the present inventors, have been to use rigorously purified zinc pyrithione, as disclosed in co-pending U.S. application Ser. No. 07/644,015, or to add amines or esterified rosin, as disclosed in co-pending U.S. application Ser. No. 07/716,415. Since these solutions may have drawbacks such as increased cost or lack of compatibility with some paints, a new, economical solution to the problem would be highly desired by the paint manufacturing community in order to maximize flexibility in using this combination of biocides in view of its excellent biocidal activity.